This project proposes to study some aspects of morphogenesis, differentiation, and cell proliferation of the endocrine pancreas. The first part of the project includes quantitation of total population size of various islet cell types and their proliferative activity throughout the development of the rat. The second portion of the project deals with effect of glucose on the proliferation activity and population size of insulin containing beta cells in organ culture. The third portion of the project is to study the insulin synthetic and releasing activities during the developmental period from fetal to neonatal ages.